1. Field of the Invention
The present invention relates generally to electrostatic precipitator apparatus and more particularly to an automatic voltage control and SCR firing circuit for use in such apparatus to instantaneously cut off power when sparking occurs and then rapidly return the precipitator voltage to a subsparking level and gradually increase from the subsparking level to the sparking threshold.
2. Description of the Prior Art
Electrostatic precipitators and control circuits therefor are well kwown in the prior art. A typical modern version of such device and its control circuitry is generally illustrated in FIG. 1 and includes a pair of input terminals 10 across which is impressed a line voltage, a step-up transformer 12, a choke 14, a pair of SCR switches 16 and 18, and a full wave rectifier 20. One output terminal of the rectifier 20 is connected to circuit ground through the resistive element of a low resistance potentiometer 22 and the other output terminal is connected to the emitting electrodes 24 of a precipitator illustrated schematically at 26. The collecting electrode 28 of precipitator 26 is connected to circuit ground.
The firing times of the SCRs 16 and 18 are controlled by an automatic voltage control and SCR firing circuit 30 which detects sparking as a function of the transformer secondary current feedback signal obtained from the tap 32 of potentiometer 22. A prior art embodiment of a similar circuit is disclosed in the U.S. patent to Peter Gelfand, U.S. Pat. No. 3,745,749. Although circuits such as that disclosed in the Gelfand patent function well, they are relatively large in size and are relatively slow in operation due to the use of magnetic firing circuits.